The present invention relates to apparatus for forming tubing and, more particularly, to a tubing mill for roll forming fluted tubing.
Fluted tubing has come into increasing commercial acceptance for uses such as in making fence posts. Not only does the fluted tube have qreater aesthetic appeal, it also offers increased strength compared to the conventional round tube. This occurs because the bends in the fluted tube afford it greater column strength and because the fluted tube is cold worked to a greater extent in its forming process.
One method of forming fluted or corrugated tubing includes first forming a tube of round cross section and then, as one of the last steps in the formation process, passing the round tubing through a set of turk's head rollers having working surfaces carrying the fluted pattern. It will be appreciated that since these patterned rollers can only engage the outside surface of the tubing, the degree of cold working of the tubing material is limited. For further information regarding this forming method and the apparatus used in carrying it out, reference may be made to U.S. Pat. No. 3,928,997.
In another proposed process for forming fluted tubing, an essentially conventional round tube continuous roll forming mill is used with the additional preliminary step that the flat strip is passed through embossing rolls to form the fluted pattern prior to transverse bending of the strip. This process has been found unsatisfactory because the pressure applied by the breakdown or bending rolls, needed to permit subsequent processing of the tubing, for example, applying a coating to the outside surface of the tubing, is so great that substantial flattening of the fluted pattern results.